This invention relates to a method of judging quality (good or bad) of an injection molded product, and more particularly a method of judging the accuracy of the configuration and dimensions of the injection molded product.
According to a prior art method of judging the configuration of a product of an injection molding machine, a resin pressure or an injection pressure in a mold cavity is measured at different times during a pressure holding time to obtain a time function P=f(t), then this function is compared with a function P.sub.1 =f(t) which holds when a satisfactory product is obtained. Alternatively, a function T=f(t) representing a mold temperature is compared with a function T.sub.1 =f(t) representing the mold temperature at which a satisfactory product is obtained, thereby judging the quality of the molded product.
The state of the resin in the mold cavity changes in accordance with a state equation PV=RT (where P: pressure, V: volume, T: temperature and R: constant). Accordingly, where the quality of the product is judged by measuring only presssure P or temperature T as in the prior art, it has been impossible to grasp volume V.